Quality of rainwater drained by a green roof in the metropolitan region of Recife, Brazil

The objective of this study was to evaluate the potential non-potable uses that can be given to the water flowing from a green roof through the characterization of its quality using the parameters and reference values contained in the Brazilian Standard ABNT NBR 15527:2007. The research was carried out in the Garage Building of the Charles Darwin Business, for a period of five months. Fifteen samples were collected from three collection points (rainwater, irrigation, and drainage from the green roof) and evaluated. For the qualitative characterization of the waters, the physicochemical parameters hydrogen potential (pH), turbidity (TBD), apparent color (AC), free residual chlorine (FRC) and electrical conductivity (EC), in addition to the microbiological parameters total coliforms, Escherichia coli and number of heterotrophic bacteria (HB), were determined. Data were subjected to descriptive and multivariate statistical analysis. The results obtained show that the green roof contributed to the reduction of rainwater pH. The green roof drainage water had higher levels of AC and TBD due to the concentrations of suspended particles, which acted as a source of EC. The FRC values complied with the legislation in all treatments. Likewise, the microbiological parameters partially complied with the standards established by the legislation. Cluster analysis formed two distinct groups, G1 comprising HB and TBD, and G2 containing the variables pH, AC, EC, and FRC. Although the quality of the drainage water does not meet all the standards required by law, this water has the potential for reuse for non-potable purposes.